Effects of thermally induced anatase-to-rutile phase transition in MOCVD-grown TiO2 films on structural and optical properties

Titanium dioxide (TiO2) films with a thickness of 550 nm were deposited on quartz glass at 300 degreesC by metalorganic chemical vapor deposition. The effects of postannealing between 600 degreesC and 1000 degreesC were investigated on the structural and optical proper-ties of the films. X-ray diffraction patterns revealed that the anatase phase of as-grown TiO2 films began to be transformed into rutile at the annealing temperature of 900 degreesC. The TiO2 films were entirely changed to the rutile phase at 1000 degreesC. From scanning electron spectroscopy and atomic force microscopy images, it was confirmed that the microstructure of as-deposited films changed from narrow columnar grains into wide columnar ones. The surface composition of the TiO2 films, which was analyzed by X-ray photoelectron spectroscopy data, was nearly constant although the films were annealed at different temperatures, When the annealing temperature increased, the transmittance of the films decreased, whereas the refractive index and the extinction coefficient calculated by the envelope method increased at high temperature. The values of optical band gap decreased from 3.5 eV to 3.25 eV at 900 degreesC. This abrupt decrease was consistent with the anatase-to-rutile phase transition.